With the exception of water, tea is the most widely consumed of all beverages. In fact, the worldwide per capita consumption has been estimated at 0.1 litre per day.
Most of the tea consumed in the Western World is so called black tea which is obtained by harvesting new leaves of the plant Camellia sinensis and withering, rolling, enzymatically oxidizing, firing and sorting them. However the leaves can be processed without the oxidation step to produce what is known as green tea. Such tea is widely consumed in parts of the People's Republic of China, Japan, North Africa and the Middle East. In another variation oolong tea is prepared by partial oxidation. That is also commonly consumed in parts of the People's Republic of China.
Tea leaves contain a large number of enzymes, biochemical intermediates and structural elements normally associated with plant growth and photosynthesis together with substances that are responsible for the characteristics of tea itself. These include flavanols, flavanol glycosides, polyphenolic acids, caffeine, amino acids, mono- and polysaccharides, proteins, cellulose, lipids, chlorophylls and volatiles.
Flavanols or more specifically flavan-3-ols tend to constitute up to 30% of the dry weight and are known as catechins. Amongst them, epigallocatechin-3-O-gallate (herein "EGCG") is predominant (10-15% of dry weight), and the other major components are epicatechin (1-3%), epigallocatechin (3-5%) and epicatechin-3-O-gallate (3-5%). Green tea retains most of EGCG as well as other catechins, but their content in black tea is greatly reduced (ca. 5%) due to both chemical and enzymatic oxidations taking place in the black tea production to give theaflavins and thearubigins.
EGCG has been claimed to possess a variety of biological activities. Its supposed anti-tumour activities receives an increasing scientific attention. Some of the other catechins may have other useful biological activities.
Tea contains many other phenols. These include gallic acid, flavanols such as quercetin, kaemferol, myricetin, and their glycosides; and depsides such as chlorogenic acid and para-coumarylquinic acid. Some of these are believed to participate in the chemical reactions that occur during fermentation.
Green tea contains many more catechins than black tea. However despite the burgeoning health consciousness amongst may consumers green tea is usually dismissed in Western countries as being too pale and unpleasant to taste. Furthermore it is typically slow to infuse and therefore not suitable for the Western desire for convenience for the sake of quality.
The present inventors have solved these problems by preparing a leaf tea comprising a blend of a first substantially fermented tea and a second substantially unfermented tea, characterised in that the blend contains catechins and phenols in a ratio of between 0.15 to 0.4, but preferably between 0.2 and 0.3. Such a leaf tea will resemble black tea but typically possess an antioxidant activity that is 10% or more higher than that the same mass of the black tea.
Blending black and green teas is known.
In U.S. Pat. No. 4,748,033 (Syfert) 90% Tender Leaf black tea is blended with 10% Taiwanese green tea and an extract therefrom is processed to give a tea concentrate having freeze thaw stability and enhanced cold water soluble. There is no disclosure of catechin to phenol ratios.
EP 654 221 (Nestle) discloses a process for making instant black tea that involves blending green and black teas in mixtures of 4:1 to 2:1. But there is no disclosure of catechin to phenol ratios or any apparent selection of teas.
SU 1,102,554 (Tea Industrial Research Institute) discloses a method for making a tea concentrate that involves extracting a mixture of fermented and unfermented tea in ratios of 1:1 to 4:1. This apparently provides an improvement in taste and aroma.
SU 1,364,269 (Tea Industrial Research Institute) discloses adding green Baikhal tea to black Baikhal tea to improve the organoleptic properties of the final products. Once again there is no discussion of catechin to phenol content.
SU 1,165,346 (Khoperiya) discloses a method for improving the quality of tea. This involves blending low grade green and black bulk tea, moistening the mixture to 10-15% water content, then drying and heating it. There is no mention of catechin to phenol ratios.
British patent specification GB-A-04831 (Jackson) discloses a method for improving the `richness` of tea and neutralising the action of tannin. This involves blending tea with a preparation of flour, grapes and nutes. Once again there is no mention of catechin to phenol ratios. It is not clear whether the tea is green or black.
The present invention however involves carefully selecting certain black and certain green teas and blending them to provide a rapidly infusible leaf tea product from which one can prepare a beverage that has an uncharateristically high amount of catechins and an enhanced antioxidant activity but still resembles black tea.